It is known that triglycerides of poly-unsaturated fatty acid (PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have beneficial medical effects, and within the last decade much attention has been directed to methods of producing triglyceride compositions with a high content of these acids, and particularly a high content of triglycerides with three such acids in the molecule.
PUFA in the form of free fatty acid or lower alkyl (e.g. methyl or ethyl) ester is available in high purity and have been used to prepare triglycerides with high PUFA content.
Thus, JP-A 61-43143 (Nisshin Flour Mill et al.) and EP 300,844 (R. F. Azar et al.) describe chemical interesterification of lower alkyl PUFA ester with triacetin or tributyrin. Sodium methylate was used as catalyst, and vacuum was used to remove lower alkyl acetate or butyrate formed in the reaction. The former describes production of triglyceride with 90% PUFA content.
JP-A 61-246146 (Nissui Seiyaku) describes halogenation of PUFA free acid, followed by reaction of PUFA acyl chloride with glycerine. The first step was carried out with oxalyl chloride at 65.degree.-90.degree. C. for 4 hours, and the second step under reflux for several hours in chloroform in the presence of quinoline or pyridine.
The above-mentioned processes use highly reactive chemicals that require special precautions in handling, these reactive chemicals react with part of the labile PUFA acyl groups, and the resulting reaction mixture in each case requires complex purification.
JP-A 62-91188 (Nisshin Oil) describes lipase-catalyzed production of PUFA glycerides from glycerol and PUFA free acid or ethyl ester, using positionally specific lipase in native form or immobilized on a weakly basic anion exchange resin. It is stated that addition of water is necessary. After reaction and removal of unreacted fatty acid, the glyceride mixture contained at most 86% triglyceride together with at least 14% diglyceride+monoglyceride. The product contained at most 85% polyunsaturated fatty acids together with at least 15% of other fatty acids.
It is an object of the invention to provide a simple process, avoiding the use of aggressive chemicals, to produce triglyceride with a low content of mono- and diglycerides, having a high content of PUFA, especially a high content of triglycerides with three PUFA in the molecule. It is also an object to provide triglyceride compositions with high PUFA content.